Hydrogeochemical indication of multistage groundwater flow system in
arid and semi-arid regions: A case study of Aksu River basin, Xinjiang,
China
Abstract
In arid and semi-arid areas, groundwater flow is a potent geological
agent. The typical profile of Aksu river basin was chosen as the
research object. First, the survey region’s geological background and
hydrological conditions were systematically analysed. Combined with
geophysical and remote sensing characteristics, the thickness change of
the Quaternary loose layer, boundary of the subaqueous system, and
basement of the water circulation depth were revealed. Hydrogeochemistry
and environmental isotopes were applied to explain the
recharge-runoff-discharge process, water-rock interaction, movement law,
and residence time of surface-groundwater. Owing to the dissolution of
carbonate and gypsum minerals and evaporates, cation exchange between Ca
2+ (Mg 2+) and Na
+ (K +), and the
evaporation-concentration effect, specific ions (SO 4
2-, Cl -, Na +)
and [total dissolved solids](javascript:;)(TDS) from the surface to
groundwater gradually increased with the flow direction and gradually
decreased with depth. This difference was more evident in the downstream
discharge area, which indicated that they belonged to different
groundwater flow systems(GFSs).Because of the elevation effect of the
recharge source, the δ 18O values in different
sections showed different degrees of depletion in the horizontal and
vertical directions. In [association with](javascript:;) the
structural ‘one convex and two concaves’ frameworks and the particle
size variation of loose sediments, it reflected the distribution pattern
of multiple local GFSs. The vertical zonation between the
3H and 14C isotope concentrations
and the recorded groundwater [residence](javascript:;) time
(modern-24000years) further illustrated the existence of intermediate
and regional GFSs. Three surface-conversion boundary key zone (GFS
cbz) were identified, and the GFS conceptual model was
established. Finally, the corresponding relationship between the GFSs
and the environmental effects, such as the distribution and aggregation
of phreatic water with high F and As and soil salinization, were
analysed, which had important theoretical significance for protecting
the ecological balance of Aksu River basin.